Vehicle systems may include various vacuum consumption devices that are actuated using vacuum. These may include, for example, a brake booster. Vacuum used by these devices may be provided by a dedicated vacuum pump. In still other embodiments, one or more aspirators (alternatively referred to as ejectors, venturi pumps, jet pumps, and eductors) may be coupled in the engine system that may harness engine airflow and use it to generate vacuum.
Since aspirators are passive devices, they provide low-cost vacuum generation when utilized in engine systems. An amount of vacuum generated at an aspirator can be controlled by controlling the motive air flow rate through the aspirator. For example, when incorporated in an engine intake system, aspirators may generate vacuum using energy that would otherwise be lost to throttling. While aspirators may generate vacuum at a lower cost and with improved efficiency as compared to electrically-driven or engine-driven vacuum pumps, their use in engine intake systems has traditionally been constrained by both available intake manifold vacuum and maximum throttle bypass flow. Some approaches for addressing this issue involve arranging a valve in series with an aspirator, or incorporating a valve into the structure of an aspirator. Such valves may be referred to as aspirator shut-off valves (ASOVs). An opening amount of the valve is controlled to control the motive air flow rate through the aspirator, and thereby control an amount of vacuum generated at the aspirator. By controlling the opening amount of the valve, the amount of air flowing through the aspirator and the suction air flow rate can be varied, thereby adjusting vacuum generation as engine operating conditions such as intake manifold pressure change.
Vacuum generation at an intake aspirator can also be enhanced by increasing the flow rate through the throat of the aspirator. In one example, this may be achieved by increasing a size (e.g., diameter) of a passage or tube directing airflow into (or out of) the aspirator. However, the inventors have recognized that such adjustments may lead to objectionable noise being transmitted to the vehicle cabin. For example, tubes leading into or out of the intake aspirator may cause a loud hissing noise to be conducted from the aspirator into the brake booster and thereon into the vehicle cabin. The noise is generated due to sonic flow of air in the aspirator throat becoming supersonic in the entrainment zone and diverging cone of the aspirator. When the supersonic flow collapses to a subsonic flow, a hissing noise is created. The noise may be objectionable to the vehicle operator and may degrade their drive experience.
The above issues may be addressed by a method of operating a valved intake aspirator that enhances vacuum generation while reducing objectionable noise production. One example method includes: closing a first valve coupled between a vacuum reservoir and an intake manifold, upstream of an aspirator, responsive to opening of a second valve coupled between the vacuum reservoir and the intake manifold. Herein, the first valve controls motive flow through the aspirator into a low pressure sink, in this case, the intake manifold. In this way, motive flow through the aspirator is disabled during conditions when hissing sound may be transmitted through the first valve when it is in the open position. In other words, the ASOV is commanded closed while conditions are such that the bypass valve is inferred to be open. The bypass valve is typically a check valve.
As an example, an engine system may be configured with an aspirator coupled across an intake throttle in a first intake bypass passage. The intake bypass passage may be configured to route a portion of intake air from upstream of an intake compressor to downstream of the intake throttle. A solenoid-operated aspirator shut-off valve (ASOV) may be coupled upstream of the aspirator in the intake bypass passage to vary a motive flow through the aspirator. An opening or closing of the vacuum solenoid may be adjusted by an engine controller based on various engine operating conditions such as manifold pressure, boost pressure, brake booster vacuum level, engine vacuum demand, etc. The aspirator throat may be coupled to a vacuum consumer, such as a brake booster, so that vacuum generated at the aspirator can be used for meeting brake vacuum demand. A further bypass passage may couple the brake booster to the intake manifold at a location downstream of the aspirator outlet. A check valve in the bypass passage may open during selected conditions, such as when intake manifold vacuum is deeper than brake booster vacuum, to substantially equalize brake booster vacuum with intake manifold vacuum.
The inventors have recognized that an objectionable hissing noise may be generated at the aspirator throat and transmitted downstream of the point when flow occurs (i.e. when the ASOV is open). This noise is transmitted through the open bypass check valve through a conduit to the brake booster. The noise cannot be transmitted upstream to the vehicle cabin through the aspirator throat due to sonic conditions at the throat. Therefore, during conditions when vacuum is demanded, ASOV opening is delayed until bypass check valve closure is inferred. An engine controller may infer an open or closed state of the bypass check valve based on an intake manifold vacuum (as estimated by a manifold pressure sensor) relative to a brake booster vacuum (as estimated by a brake booster pressure sensor). In response to the vacuum demand, the controller may first allow a vacuum to be drawn at the brake booster from the intake manifold via the bypass check valve with the ASOV closed. Upon inferring that the bypass check valve is closed, the ASOV may be opened, motive flow may be directed through the aspirator, and vacuum may be drawn into the brake booster from the aspirator throat.
In this way, by closing an ASOV during conditions when a bypass check valve is open, the transmission of the hissing noise associated with vacuum production at the aspirator during those conditions is reduced. By delaying motive flow through the aspirator until the bypass check valve is closed, generation and transmission of objectionable noise resulting from aspirator vacuum production is decreased. Overall, the aspirator is able to meet the brake vacuum demand at a lower cost and with improved efficiency without degrading the vehicle operator's drive experience.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.